Download Background Lecture - IEEE Real World Engineering Projects

Feedback
F
db k C
Controlled
t ll d
Brushless DC Motor with
Personal Electric Vehicle
Application
Background Lecture
What is a motor?
A motor converts electric energy to rotating mechanical energy.
Electric Energy
Input
voltage and current
Energy
Converter
typical:
magnetic field
Rotating Mechanical
Energy Output
speed
p
and torque
q
What are motors used for?
What are motors used for?
Rotating action mo
moves
es
loads
• Material-movers
– Fans, pumps,
conveyors robots
conveyors,
• People-movers
– Elevators, escalators,
moving walkways
– Hybrid
y
cars,, buses,,
electric motorcycles,
personal transporters
( g y)
(Segway)
What are motors used for?
Rotating action mo
moves
es
loads
• Material-movers
– Fans, pumps,
conveyors robots
conveyors,
• People-movers
– Elevators, escalators,
moving walkways
– Hybrid
y
cars,, buses,,
electric motorcycles,
personal transporters
( g y)
(Segway)
Personal Electric Vehicles
New Transportation Alternative
•
•
•
•
Single passenger
1-10km
1
10km trips
Open to weather
Less-than-highway speeds
up to 50
50km/hr
/
• Purchase cost US$2000 up
t US$100,000
to
US$100 000
PEVs Potential Impact on Society
• Reduced greenhouse gas emission versus
cars
• Higher fuel efficiency versus cars
How much CO2 comes from one gallon
(6.3lbs) of automobile gasoline?
• Wh
When gasoline
li b
burns, th
the carbon
b
and hydrogen separate.
• The hydrogen combines with oxygen
to form water (H2O), and carbon
combines with oxygen to form
carbon dioxide (CO2).
• A carbon atom has a weight of 12,
and each oxygen atom has a weight
of 16, giving each single molecule of
CO2 an atomic
t i weight
i ht off 44 (12 ffrom
carbon and 32 from oxygen).
How much CO2 comes from one gallon
(6.3lbs) of automobile gasoline?
• T
To calculate
l l t th
the amountt off CO2
produced from a gallon of gasoline, the
g of the carbon in the g
gasoline is
weight
multiplied by 44/12 or 3.7
• Since gasoline is about 87% carbon and
13% hydrogen
h d
by
b weight,
i ht the
th carbon
b iin a
gallon of gasoline weighs 5.5 pounds (6.3
lbs.
bs x .87).
8 )
• Multiply the weight of the carbon (5.5
pounds) by 3.7, which equals
20 p
pounds of CO2!
Since PEVs are electric, do they
produce CO2?
• N
Nott di
directly.
tl Th
The CO2
produced by electric
power plants must be
accounted for.
• For the 2004 fuel mix
of US electricity
production,, the
p
average CO2
produced is
1.55 lbs CO2 per kWh
What is CO2 production per
passenger mile?
• If an automobile gets 20 miles/gallon, then
calculate the CO2 p
produced p
per g
gallon.
• You will further explore this question in the
assignment
Barriers to PEV Adoption
• New technology
• Battery energy density and acquisition
cost
– Recent
R
t advances
d
d
driven
i
b
by cellll phone
h
market
k t
• Production economies
• Local traffic laws
• Weather
W th inconvenience
i
i
PEV Advantages Over Cars
• Si
Significantly
ifi
tl higher
hi h fuel
f l efficiency
ffi i
on a perpassenger mile basis
• Significantly reduced greenhouse gas
emission
• Reduced congestion in high density urban
areas
– London, Manhattan per car entry fee
• Shorter trip times in high density urban areas
• Quieter
Does anyone have a motor with them?
What is it used for?
Can we see it?
Does it operate from a dc or ac power
source?
Motor names
• (Brushed) DC motors
• Brushless DC motors
• AC motors
– Induction motors
– Synchronous motors
(generators)
Types of voltage inputs
• DC (direct current)
– Voltage
g does not vary
y with time
• AC
C ((alternating current))
– Voltage
g changes
g varies over time
– Typically a sinusoid, but maybe not
How do motors work?
One explanation:
Electric current interacts with magnetic field
to produce torque on a shaft
Another:
ot e
Two magnetic fields interact to produce
t
torque
on a shaft
h ft
How does a (brushed) DC motor work?
(Brushed) DC Motor from RC Car
How does a brushless DC motor work?
N
Switch state:
If magnet near coil, ON
Else OFF
Why doesn’t rotor stop
when coil is off?
BLDC you will build
The components of an Aveox 36/30/1.5 brushless motor.
How does the switch know if
there is a magnet nearby?
• Use a switch that detects a magnetic field
Magnetic
g
reed switch
• Use a sensor that detects a magnetic field
and commands another switch
Hall-effect sensor and transistor
• Use a sensor that optically detects the rotor
position and commands another switch
p
Optical encoder and transistor
How does the switch know if
there is a magnet nearby?
• Use a switch that detects a magnetic field
Magnetic
g
reed switch
• Use a sensor that detects a magnetic field
and commands another switch
Hall-effect sensor and transistor
• Use a sensor that optically detects the rotor
position and commands another switch
p
Optical encoder and transistor
How does the switch know if
there is a magnet nearby?
• Use a switch that detects a magnetic field
Magnetic
g
reed switch
• Use a sensor that detects a magnetic field
and commands another switch
Hall-effect sensor and transistor
• Use a sensor that optically detects the rotor
position and commands another switch
p
Optical encoder and transistor
Reed Switch BLDC Schematic
N
1.5V
COIL
1.5V
1.5V
Reed
switch
1.5V
Reed Switch Technology
T i l rating:
Typical
ti
sw
108
failure
MTBF: mean time
between failure
How long will a typical reed switch last continuously operating a
four pole rotor BLDC at 1000rpm?
Reed Switch Technology
Typical rating:
sw
8
10
failure
How long will a typical reed switch last continuously operating a
f
four
pole
l rotor
t BLDC att 1000
1000rpm?
?
rev ⎞ ⎛ sw ⎞
⎛
3 sw
1000
4
4
10
=
⋅
⎜
min ⎟⎠ ⎜⎝ rev ⎟⎠
min
⎝
⎛ 8 sw ⎞ ⎛ min ⎞
3 min
10
25
10
=
⋅
⎜
failure ⎟⎠ ⎜⎝ 4 ⋅ 103 sw ⎟⎠
failure
⎝
(416 hours or 1.14 years)
What if we want to continuously
operate for more than one year?
N
1.5V
COIL
1.5V
1.5V
Reed
switch
1.5V
What if we want to continuously
operate for more than one year?
Solution:
replace
p
the reed switch with a transistor
Typical
T
i l ttransistor
i t MTBF iis >100,000’s
100 000’ h
hours
(e.g.,
(e
g , 200,000
00,000 hours
ou s or
o 23
3 years)
yea s)
What are the terminals on a
transistor?
Th switch
The
it h iis b
between
t
emitter
itt and
d collector.
ll t
The base controls the state of the switch.
Use transistor as a switch
1.5V
N
1.5V
1.5V
1.5V
TIP106
base
What’s missing?
Add magnetic sensor to command
transistor to switch
Hall-effect sensor
Where
are H
Hall-effect
Wh
ll ff t sensors used
d
(besides) BLDCs?
Add magnetic sensor to command
transistor to switch
Hall-effect sensor
Where
are H
Hall-effect
Wh
ll ff t sensors used
d
(besides) BLDCs?
S
Speedometers
d
t
on bi
bicycles.
l
Why not build this circuit?
COIL
Coil resistance about 4 ohms.
COIL
Why not build this circuit?
Coil resistance about 4 ohms.
V 6
coil current ≅ = = 1.5A
R 4
COIL
Power Transistor Amplifies
Coil circuit switched by
power transistor with Hall
effect sensor
Precision BLDC using optical
encoder
Optical Switch
What should be the
angle between one
encoder tab and a
rotor magnet?
Optek OPB870
Optical Encoder BLDC Schematic
COIL
1.5V
k
Coil circuit switched by
power transistor with
slotted optical sensor
1.5V
1.5V
TIP106
1.5V
OPB800
Optical switch
How does a BLDC motor make a
difference in PEV’s?
• Higher power to weight ratio
– BLDC: 2000 W/kg
– Brushed DC: 1000 W/kg
• Higher efficiency in converting electric energy to rotating
mechanical energy
– BLDC: >90%
– Brushed DC: 75%
• Lower maintenance
– BLDC: no regular maintenance
– Brushed DC: replace brushes
• Lower gear-ratio transmission
– BLDC: 5:1@2500rpm,
5:1@2500rpm typically single
single-stage
stage
– Brushed DC: 20:1 @10,000rpm, typically two-stage
Drawbacks to BLDC versus
Brushed DC
• Higher acquisition cost
– BLDC with electronic controller about 50%
%
higher for 1.5hp
• High magnetic field strength permanent
magnets on rotor
Your assignment
• B
Build
ild your own BLDC
• Read articles:
– Ul
Ulrich,
i h “Estimating
“E ti ti the
th Technology
T h l
F
Frontier
ti ffor
Personal Electric Vehicles”
– Heinzmann and Taylor
Taylor, “The
The Role of the Segway
Personal Transporter in Emissions Reduction and
Energy Efficiency”
• Discover the potential impact of PEVs on
greenhouse gas emissions and fuel usage
• Write
W it a 2-3
2 3 page reportt on your BLDC and
d
your discoveries